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.TH SETSID 2 "Aug 21, 2002"
.SH NAME
setsid \- create session and set process group ID
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <unistd.h>

\fBpid_t\fR \fBsetsid\fR(\fBvoid\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsetsid()\fR function creates a new session, if the calling process is
not a process group leader. Upon return the calling process will be the session
leader of this new session, will be the process group leader of a new process
group, and will have no controlling terminal. The process group  \fBID\fR of
the calling process will be set equal to the process \fBID\fR of the calling
process. The calling process will be the only process in the new process group
and the only process in the new session.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBsetsid()\fR returns the value of the process
group  \fBID\fR of the calling process. Otherwise it returns \fB(pid_t)\(mi1\fR
and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The \fBsetsid()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 9n
The calling process is already a process group leader, or the process group
\fBID\fR of a process other than the calling process matches the process
\fBID\fR of the calling process.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	Async-Signal-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR getsid (2),
.BR setpgid (2),
.BR setpgrp (2),
.BR attributes (7),
.BR standards (7)
.SH WARNINGS
.sp
.LP
A call to \fBsetsid()\fR by a process that is a process group leader will fail.
A process can become a process group leader by being the last member of a
pipeline started by a job control shell. Thus, a process that expects to be
part of a pipeline, and that calls \fBsetsid()\fR, should always first fork;
the parent should exit and the child should call \fBsetsid()\fR. This will
ensure that the calling process will work reliably when started by both job
control shells and non-job control shells.
